Pathology
Newton’s First Law of Motion states that an object at rest will have a tendency to stay at rest unless acted upon by an outside force. If you are sitting still at a traffic light and someone hits you from behind, your head will have a tendency to stay at rest when the force of the impact first throws the car (and your body) in a forward direction. This will make your head hyperextend in relation to the rest of your body. This is an acceleration injury. A similar situation happens in the deceleration injury.

Newton’s first law also states that an object in motion will have a tendency to stay in motion unless acted upon by an outside force. If you are moving forward in a car and you hit something head-on, there is a sudden deceleration of both the car and your body. Your head is ?floating? on top of your torso, so it is more moveable in relation to the torso. When your body suddenly stops as a result of hitting something straight in front of you, your head keeps going - and it is the soft tissues of the posterior cervical area that will have to stop it. The posterior cervical muscles are likely to be strained in the process. This is a deceleration whiplash injury.

These examples may be quite simplified in relation to what actually happens in many motor-vehicle accidents. Many collisions don’t occur either straight on or from behind. An impact from another angle changes where the cervical region may be stressed. In addition, the speed or velocity of the impact is often not directly consistent with the degree of tissue damage. It has been demonstrated that even in a low-velocity impact, the head may extend past 120 degrees of extension where normal extension is 70 degrees.

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